A nozzle used for feeding from a vessel to another prevents chemical reactions between air and the metal and also prevents the heat loss by a radiation of the molten metal. Meanwhile the nozzle is abraded by a molten metal due to a thermal stress and hence a life of a nozzle limits the casting time in continuous casting. A conventional nozzle, insert and removal device (hereafter called nozzle exchange device) give a solution to overcome the limit of casting time of a nozzle), for example U.S. Pat. No. 4,669,528.
For example when the outer surface of a nozzle at the level of meniscus reaches a certain level or a breakage of the nozzle occurs, the casting is stopped and the eroded nozzle is exchanged for a new one in a short period and the casting continues. Normally the nozzle is made up of alumina-graphite and the nozzle comprises a flange or a plate (hereafter called flange or plate) connected to a cylinder hereunder and outlet holes on both sides of the cylinder.
More exactly speaking a nozzle is provided with a tubular channel and a flange plate with a casting hole. The plate is connected with the upper nozzle constituting a feeding channel of a molten metal to the nozzle. The plate is provided with the upper surface and the down surface, which is connected to supporting surfaces provided on the both side of nozzle holes.
The nozzle is able to slide between an upper nozzle feeding molten metal from a tundish, a bottom plate attached to the upper nozzle or a fixed plate attached with casting control device and a lower flat plate.
In this text a casting nozzle does not means an upper nozzle fixed to a tundish but a nozzle being able to slide in the nozzle exchange device.
PCT WO 00/32337 discloses a refractory nozzle provided with a shock absorbing intermediate region between a metal case and the refractory part of nozzle.
The region is filled up with a material which is solid in an ambient temperature and deformable at a high temperature. Hence the space functions to reduce a thermo-mechanical stress and micro-cracks, occurring at the beginning of casting operation.
The disclosed nozzle is a nozzle being able to slide in an exchange device and is supported by an upward stress.
The nozzle is provided with a tapered part which is supported by an upward thrust to fasten the nozzle with the upper nozzle.
The thrust is generated by a spring or a locker, whereby the nozzle is fastened with an upper refractory material or an upper nozzle.
A casting nozzle is made of a mono-block or of combination of a few refractory parts. The upper part of nozzle with a flange and an upper tubular part of nozzle can be protected by a metal case.
However a conjunction between a tubular part and a flange exhibits cracks and micro-cracks, which occur during the use of a nozzle due to thermal stress or thermo-mechanical stress. Such cracks might be caused by a force to maintain the nozzle within the device and by vibration caused by flow of molten metal through the nozzle.
Such cracks cause breakage of the nozzle. The throttling of nozzle induces a lower pressure which causes suction of air, whereby oxygen and nitrogen in the air are contaminated in the molten metal or molten steel.
Further the refractory is damaged and cracked in combination of oxygen and high temperature, which accelerates micro degradation and finally suspends a casting operation.
Some methods have been proposed to enhance a resistance of cracks of a nozzle. Some refractory are known, which have a superior resistance against cracks.
However, those materials are sensitive to erosion or corrosion. Such means and other improvement enhance the life of casting nozzle.
Yet, there remains still the some problems to be solved.
Conventional nozzle exchange device causes a bending stress at the neck between the upper flange or plate and a tubular part, which induces cracks at the neck. And the plate is apt to deform along the axis parallel with the guided direction of plate.
Hence, E P 1590114 B1 (Japanese publication No. 2006-515803) discloses a casting nozzle (1), as disclosed in FIG. 1, having a flange or a plate (hereafter called plate), and a rear side having two inclined surface (3, 5) with different angles, which may prevent cracks.
The example is not protected with a metal case against the upward force on the metal case. The plate is, as is disclosed in FIG. 2, supported by springs exerting an upward force on an inclined surface (5).
In addition an upper casting nozzle (7) is fixed by a fixing plate (8).
The above solution intends to prevent the bending stress or to lessen the bending stress, which is contributed by a design of nozzle or an assembling process. However, cracks (10, 11, 12) are apt to occur in operation as shown in FIG. 3. The reason is suspected to be forces induced and directed to upward or horizontal direction due to a small thrust plate (9).
Therefore a frequent breakage of a casting nozzle occurs and the casting is suspended. Hence a more stable casting operation is intended by improvement of nozzle life, which leads to a new type of nozzle design.